Re: [PATCH v6 6/9] ACPI: CPPC: add APIs and sysfs interface for min/max_perf
From: Sumit Gupta
Date: Sat Jan 24 2026 - 15:32:57 EST
On 22/01/26 17:06, Pierre Gondois wrote:
External email: Use caution opening links or attachments
On 1/20/26 15:56, Sumit Gupta wrote:
Add cppc_get/set_min_perf() and cppc_get/set_max_perf() APIs to read and
write the MIN_PERF and MAX_PERF registers.
Also add sysfs interfaces (min_perf, max_perf) in cppc_cpufreq driver
to expose these controls to userspace. The sysfs values are in frequency
(kHz) for consistency with other cpufreq sysfs files.
A mutex is used to serialize sysfs store operations to ensure hardware
register writes and perf_ctrls updates are atomic.
Signed-off-by: Sumit Gupta <sumitg@xxxxxxxxxx>
---
drivers/acpi/cppc_acpi.c | 44 +++++++++
drivers/cpufreq/cppc_cpufreq.c | 157 +++++++++++++++++++++++++++++++++
include/acpi/cppc_acpi.h | 20 +++++
3 files changed, 221 insertions(+)
diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 45c6bd6ec24b..46bf45f8b0f3 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -1743,6 +1743,50 @@ int cppc_set_auto_sel(int cpu, bool enable)
}
EXPORT_SYMBOL_GPL(cppc_set_auto_sel);
+/**
+ * cppc_get_min_perf - Read minimum performance register.
+ * @cpu: CPU from which to read register.
+ * @min_perf: Return address.
+ */
+int cppc_get_min_perf(int cpu, u64 *min_perf)
+{
+ return cppc_get_reg_val(cpu, MIN_PERF, min_perf);
+}
+EXPORT_SYMBOL_GPL(cppc_get_min_perf);
+
+/**
+ * cppc_set_min_perf - Write minimum performance register.
+ * @cpu: CPU to which to write register.
+ * @min_perf: the desired minimum performance value to be updated.
+ */
+int cppc_set_min_perf(int cpu, u32 min_perf)
+{
+ return cppc_set_reg_val(cpu, MIN_PERF, min_perf);
+}
+EXPORT_SYMBOL_GPL(cppc_set_min_perf);
+
+/**
+ * cppc_get_max_perf - Read maximum performance register.
+ * @cpu: CPU from which to read register.
+ * @max_perf: Return address.
+ */
+int cppc_get_max_perf(int cpu, u64 *max_perf)
+{
+ return cppc_get_reg_val(cpu, MAX_PERF, max_perf);
+}
+EXPORT_SYMBOL_GPL(cppc_get_max_perf);
+
+/**
+ * cppc_set_max_perf - Write maximum performance register.
+ * @cpu: CPU to which to write register.
+ * @max_perf: the desired maximum performance value to be updated.
+ */
+int cppc_set_max_perf(int cpu, u32 max_perf)
+{
+ return cppc_set_reg_val(cpu, MAX_PERF, max_perf);
+}
+EXPORT_SYMBOL_GPL(cppc_set_max_perf);
+
/**
* cppc_set_enable - Set to enable CPPC on the processor by writing the
* Continuous Performance Control package EnableRegister field.
diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 229880c4eedb..66e183b45fb0 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -28,6 +28,8 @@
static struct cpufreq_driver cppc_cpufreq_driver;
+static DEFINE_MUTEX(cppc_cpufreq_autonomous_lock);
+
Shouldn't concurrent access be handled by the policy->rwsem ?
I think this can be checked using either:
- lockdep_assert_held_write(&policy->rwsem)
- lockdep_assert_held_read(&policy->rwsem)
in store/show_max_perf() for instance.
You're right. The cpufreq sysfs already holds policy->rwsem for
show/store callbacks. I'll remove the mutex and add lockdep
assertions for the expected locking.
--------
File: drivers/cpufreq/cpufreq.c
static ssize_t store(struct kobject *kobj, struct attribute *attr,
const char *buf, size_t count)
{
struct cpufreq_policy *policy = to_policy(kobj);
....
guard(cpufreq_policy_write)(policy);
--------
Thank you,
Sumit Gupta
#ifdef CONFIG_ACPI_CPPC_CPUFREQ_FIE
static enum {
FIE_UNSET = -1,
@@ -570,6 +572,35 @@ static void populate_efficiency_class(void)
}
#endif
+/* Set min/max performance HW register and cache the value */
+static int cppc_cpufreq_set_mperf_reg(struct cpufreq_policy *policy,
+ u64 val, bool is_min)
+{
+ struct cppc_cpudata *cpu_data = policy->driver_data;
+ struct cppc_perf_caps *caps = &cpu_data->perf_caps;
+ unsigned int cpu = policy->cpu;
+ u32 perf;
+ int ret;
+
+ perf = clamp(val, caps->lowest_perf, caps->highest_perf);
+
+ ret = is_min ? cppc_set_min_perf(cpu, perf) :
+ cppc_set_max_perf(cpu, perf);
+ if (ret) {
+ if (ret != -EOPNOTSUPP)
+ pr_warn("CPU%d: set %s_perf=%u failed (%d)\n",
+ cpu, is_min ? "min" : "max", perf, ret);
+ return ret;
+ }
+
+ if (is_min)
+ cpu_data->perf_ctrls.min_perf = perf;
+ else
+ cpu_data->perf_ctrls.max_perf = perf;
+
+ return 0;
+}
+
static struct cppc_cpudata *cppc_cpufreq_get_cpu_data(unsigned int cpu)
{
struct cppc_cpudata *cpu_data;
@@ -918,16 +949,142 @@ CPPC_CPUFREQ_ATTR_RW_U64(auto_act_window, cppc_get_auto_act_window,
CPPC_CPUFREQ_ATTR_RW_U64(energy_performance_preference_val,
cppc_get_epp_perf, cppc_set_epp)
+/**
+ * show_min_perf - Show minimum performance as frequency (kHz)
+ * @policy: cpufreq policy
+ * @buf: buffer to write the frequency value to
+ *
+ * Reads the MIN_PERF register and converts the performance value to
+ * frequency (kHz).
+ */
+static ssize_t show_min_perf(struct cpufreq_policy *policy, char *buf)
+{
+ struct cppc_cpudata *cpu_data = policy->driver_data;
+ struct cppc_perf_caps *caps = &cpu_data->perf_caps;
+ u64 perf;
+ int ret;
+
+ ret = cppc_get_min_perf(policy->cpu, &perf);
+ if (ret == -EOPNOTSUPP)
+ return sysfs_emit(buf, "<unsupported>\n");
+ if (ret)
+ return ret;
+
+ /* Use lowest_perf if register is uninitialized (0) */
+ if (perf == 0)
+ perf = caps->lowest_perf;
+
+ /* Convert performance to frequency (kHz) for user */
+ return sysfs_emit(buf, "%u\n", cppc_perf_to_khz(caps, perf));
+}
+
+/**
+ * store_min_perf - Set minimum performance from frequency (kHz)
+ * @policy: cpufreq policy
+ * @buf: buffer containing the frequency value
+ * @count: size of @buf
+ *
+ * Converts the user-provided frequency (kHz) to a performance value
+ * and writes it to the MIN_PERF register.
+ */
+static ssize_t store_min_perf(struct cpufreq_policy *policy, const char *buf,
+ size_t count)
+{
+ struct cppc_cpudata *cpu_data = policy->driver_data;
+ unsigned int freq_khz;
+ u64 perf;
+ int ret;
+
+ ret = kstrtouint(buf, 0, &freq_khz);
+ if (ret)
+ return ret;
+
+ /* Convert frequency (kHz) to performance value */
+ perf = cppc_khz_to_perf(&cpu_data->perf_caps, freq_khz);
+
+ guard(mutex)(&cppc_cpufreq_autonomous_lock);
+ ret = cppc_cpufreq_set_mperf_reg(policy, perf, true);
+ if (ret)
+ return ret;
+
+ return count;
+}
+
+/**
+ * show_max_perf - Show maximum performance as frequency (kHz)
+ * @policy: cpufreq policy
+ * @buf: buffer to write the frequency value to
+ *
+ * Reads the MAX_PERF register and converts the performance value to
+ * frequency (kHz).
+ */
+static ssize_t show_max_perf(struct cpufreq_policy *policy, char *buf)
+{
+ struct cppc_cpudata *cpu_data = policy->driver_data;
+ struct cppc_perf_caps *caps = &cpu_data->perf_caps;
+ u64 perf;
+ int ret;
+
+ ret = cppc_get_max_perf(policy->cpu, &perf);
+ if (ret == -EOPNOTSUPP)
+ return sysfs_emit(buf, "<unsupported>\n");
+ if (ret)
+ return ret;
+
+ /* Use highest_perf if register is uninitialized or out of range */
+ if (perf == 0 || perf > caps->highest_perf)
+ perf = caps->highest_perf;
+
+ /* Convert performance to frequency (kHz) for user */
+ return sysfs_emit(buf, "%u\n", cppc_perf_to_khz(caps, perf));
+}
+
+/**
+ * store_max_perf - Set maximum performance from frequency (kHz)
+ * @policy: cpufreq policy
+ * @buf: buffer containing the frequency value
+ * @count: size of @buf
+ *
+ * Converts the user-provided frequency (kHz) to a performance value
+ * and writes it to the MAX_PERF register.
+ */
+static ssize_t store_max_perf(struct cpufreq_policy *policy, const char *buf,
+ size_t count)
+{
+ struct cppc_cpudata *cpu_data = policy->driver_data;
+ unsigned int freq_khz;
+ u64 perf;
+ int ret;
+
+ ret = kstrtouint(buf, 0, &freq_khz);
+ if (ret)
+ return ret;
+
+ /* Convert frequency (kHz) to performance value */
+ perf = cppc_khz_to_perf(&cpu_data->perf_caps, freq_khz);
+
+ guard(mutex)(&cppc_cpufreq_autonomous_lock);
+ ret = cppc_cpufreq_set_mperf_reg(policy, perf, false);
+ if (ret)
+ return ret;
+
+ return count;
+}
+
cpufreq_freq_attr_ro(freqdomain_cpus);
cpufreq_freq_attr_rw(auto_select);
cpufreq_freq_attr_rw(auto_act_window);
cpufreq_freq_attr_rw(energy_performance_preference_val);
+cpufreq_freq_attr_rw(min_perf);
+cpufreq_freq_attr_rw(max_perf);
static struct freq_attr *cppc_cpufreq_attr[] = {
&freqdomain_cpus,
&auto_select,
&auto_act_window,
&energy_performance_preference_val,
+ &min_perf,
+ &max_perf,
NULL,
};
diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
index 3fc796c0d902..b358440cd0e2 100644
--- a/include/acpi/cppc_acpi.h
+++ b/include/acpi/cppc_acpi.h
@@ -174,6 +174,10 @@ extern int cppc_get_auto_act_window(int cpu, u64 *auto_act_window);
extern int cppc_set_auto_act_window(int cpu, u64 auto_act_window);
extern int cppc_get_auto_sel(int cpu, bool *enable);
extern int cppc_set_auto_sel(int cpu, bool enable);
+extern int cppc_get_min_perf(int cpu, u64 *min_perf);
+extern int cppc_set_min_perf(int cpu, u32 min_perf);
+extern int cppc_get_max_perf(int cpu, u64 *max_perf);
+extern int cppc_set_max_perf(int cpu, u32 max_perf);
extern int amd_get_highest_perf(unsigned int cpu, u32 *highest_perf);
extern int amd_get_boost_ratio_numerator(unsigned int cpu, u64 *numerator);
extern int amd_detect_prefcore(bool *detected);
@@ -270,6 +274,22 @@ static inline int cppc_set_auto_sel(int cpu, bool enable)
{
return -EOPNOTSUPP;
}
+static inline int cppc_get_min_perf(int cpu, u64 *min_perf)
+{
+ return -EOPNOTSUPP;
+}
+static inline int cppc_set_min_perf(int cpu, u32 min_perf)
+{
+ return -EOPNOTSUPP;
+}
+static inline int cppc_get_max_perf(int cpu, u64 *max_perf)
+{
+ return -EOPNOTSUPP;
+}
+static inline int cppc_set_max_perf(int cpu, u32 max_perf)
+{
+ return -EOPNOTSUPP;
+}
static inline int amd_get_highest_perf(unsigned int cpu, u32 *highest_perf)
{
return -ENODEV;